The invention relates to a washer to be arranged between a head of a screw and a work piece in a threaded assembly, with the washer having a bore accepting the screw and being spatially deformed around at least one axis extending diametrically through said bore.
Further, the invention relates to a threaded assembly of a screw and a work piece, with the screw having a shaft provided with a thread and at the end facing away from the head having a hole-forming or boring tip and at its end adjacent to the head a shaft section free from threads, and with the work piece comprising at least one or preferably several thin plates.
A known washer of the type mentioned at the outset is represented for example by a corrugated washer, inserted in a threaded assembly for securing the screw from loosening and inverse rotation. Such a corrugated washer is made of spring steel and is elastically deformed during the creation of the threaded assembly, i.e. when the screw is tightened. By the elastic deformation of the corrugated washer the completed threaded assembly remains pre-stressed by an elastic force effective in the direction of the axis of the screw. When in a threaded assembly a potentially existing play is to be compensated, usually washers are used having a defined thickness appropriate to the play to be compensated. Corrugated washers or the like only have a small thickness and are therefore suitable only to a very limited extent, in addition to their function of preventing inverse rotation to be used to compensate play.
A threaded assembly of the type mentioned at the outset is known from DE 197 18 712 C1. A similar threaded assembly is known from U.S. Pat. No. 2,321,379, with in this case the screw not provided with a hole forming or boring tip but merely with the end of the shaft slightly tapering. In both cases the work piece comprises two thin plates, which can be clamped towards each other in a secure manner with the help of the screw. Due to the fact that an unthreaded shaft section is formed between the head and the thread provided on the shaft being of the same size or slightly smaller than the thickness of the two thin plates to be connected to each other, the screw can be overwound after the final placement. A tight assembly of the thin plates forming the work piece without the screw being able to rotate inversely is only ensured if no play exists between the head of the screw and the work piece. For this purpose, the thickness of the work piece must be precisely equivalent to the length of the unthreaded shaft section or may be only slightly greater than the length of the unthreaded shaft section. In general, in the assembled position the two thin plates shall be held in a tightly compressed fashion. If one of the two thin plates is too thin or only one screw is available with its unthreaded shaft section being too long for the existing thickness of the work piece, play develops with no option for compensation being provided in such a threaded assembly. Due to its little thickness a securing washer, similar to a corrugated washer, could be suited to a limited extent only.
EP 0 556 438 A1 describes a screw with an elastically deforming washer for creating a threaded assembly. The elastic restoring force of the washer is used to create a fixed assembly. Even such a washer is able to compensate play to a limited extent only.